Audio reproduction has encountered and wrestled with the twin problems of maximizing dynamic range and minimizing compression since the patenting of the electro-dynamic loudspeaker by Peter Jensen in 1927. When addressing the goal of maximum fidelity to the original sound source, audio reproduction systems elements such as amplifiers and loudspeakers must aim to provide a dynamic range which equals or exceeds that of the original source signals. Where the selected available technologies do not allow sufficient dynamic range and linearity to be achieved in the reproduction, system dynamic range is lost either or both at the system minimum capability (the electronics noise floor or minimum motive force in electro-acoustic elements), or at the system maximum capability (clipping or overload). In loudspeakers, system overload can be evident in a lessening of the ratio of output to input as level nears maximum as the system looses linearity such that an increase in input is only partially reflected in an increase in output. This effect in loudspeakers is commonly referred to as power compression. A similar effect, known as signal compression, being a reduction in through gain, the ratio of output to input levels, can be deliberately introduced as a signal processing element in the electronic signal path. This latter technique has been widely used to ameliorate the deleterious effects of reproduction system overload and to allow the source dynamic range to be reduced to allow the signal program material to be reproduced without gross overload of the available sound system. As an example, a typical FM radio transmission may achieve a dynamic range on the order of 50 dB. In contrast, in a typical concert hall with a background noise level of 35 dBA performance levels can reach over 115 dBA, a dynamic range of 80 dB. The performance dynamic range exceeds the dynamic range available for an FM broadcast of the concert by 30 dB. Signal dynamic range compression must be imposed on the source signal to reduce the dynamic range to that available in the reproduction medium. An adjunct dynamic range modifier is an expander which takes the compressed signal and attempts to increase the dynamic range to more closely mimic the original source signal. An audio system that has substantial compression will typically have poor dynamic range. At higher levels, compression becomes objectionable to most listeners, and is a cue that the system performs poorly.
The typical audio amplifier is a voltage-controlled device. A typical audio amplifier will take a small time-varying input voltage (typically 50 mV peak) and will output an identical, though larger, version of the time-varying signal. The overall ratio of the output-to-input is the effective gain of the system, which is often expressed in decibels (dB). When a user increases the volume, they are, in reality, increasing the voltage output from a voltage-controlled amplifier. The voltage-controlled amplifier is limited by its voltage rail, which is, essentially, the output voltage limit. Simplistically stated, if the input times the gain exceeds the voltage rail, the output waveform is going to be distorted.
There are two common methods of addressing the problem of the input times the gain exceeding the voltage rail: clipping or compressing. Clipping refers to the output wave form being flattened anytime the input times the gain exceeds the voltage rail. Compression refers to a control mechanism, within an audio amplifier or processor, that lowers the system gain so that the gain times the input does not exceed the output. Compression is done in real-time in many audio amplifiers, meaning that the gain if varying in real time. As such, Compression is a linear distortion. Although Compression does not affect the Total Harmonic Distortion of a typical audio system, it is, nonetheless, perceptible, and objectionable, to the end-user. Compression is used in almost all audio amplifiers, with clipping being used in only the most inexpensive and lowest performing systems.
Power Compression is an artifact created by the topology and construction of most audio systems. Loudspeakers (the electrical “Load”), be they floor-standing, bookshelf, desktop, or headphone, typically are current-dependent devices, meaning that they follow Lorentz' Force Law: F=Bxli. The force (F), driving the diaphragm, is dependent on the current (i) through a length of wire (I), that is orthogonal to the magnetic field (B).
Since most electric-to-audio transducers follow Lorentz′ Law, and since most voltage-controlled amplifiers are limited by a voltage rail, dynamic range and compression become concerns for most audio systems. A useful definition of Dynamic Range is the ratio of the maximum undistorted sine wave to the noise floor, which is the level at which a useful audio signal subsides into the ambient noise of the system. Audio system limitations with respect to Dynamic Range can be measured by Crest Factor. Crest Factor is the ratio between the r.m.s. and the maximum undistorted voltage values in an audio system. From an end-user standpoint, a larger Dynamic Range is preferable. Simultaneously, at a particular listening-level (voltage), a higher Crest Factor is preferable from an end-user standpoint. Diminuendo Factor, or Decrescendo Factor, is defined in this invention as the ratio between the r.m.s. level and noise floor. For a particularly idealized system, the Diminuendo Factor plus Crest Factor, as measured in dB, should equal the Effective Dynamic Range. The Effective Dynamic Range, or the Diminuendo plus Crest Factor, are limited by the voltage rails or by problems inherent in the dynamics processor, itself. The audio volume information can only be presented as voltage variations between the noise floor and the voltage rail, which is the Effective Dynamic Range.
There are many different algorithms for implementing a compression strategy. Mostly, compression uses a limiter circuit, or a DSP which mimics a limiter circuit, and lowers the Crest Factor, so that the Effective Dynamic Range (Diminuendo Factor plus Crest Factor) is within the voltage rails. Since compression, as currently implemented, affects mostly the Crest Factor, and not the Diminuendo Factor, it colors the output of the sound.
Current technology fails to give the listener the ability to control the relative values of compression, Dynamic Range, Diminuendo Factor, and Crest Factor. These values can be measured and quantified as is presented in this system and method. Rather, the current solutions are all concerned with imposing built-in relationships between the compression, Dynamic Range, Diminuendo Factor, and Crest Factor. Furthermore, current technology fails to allow a user to measure and analyze the effects of signal dynamics modifier devices with respect to Effective Dynamic Range, Diminuendo Factor and Crest Factor.
For example, U.S. Pat. No. 8,194,869, by named inventors Ingalls, et. al. (“Ingalls '869”), entitled, “System and method for harmonizing calibration of audio between networked conference rooms,” teaches a method a power management system for an audio system in which a processor computes the real time parameters of the loudspeaker in the audio system; a threshold comparator measures the parameters, and compares them versus an estimated operation characteristic; and a limiter which can adjust the audio output signal to the amplifier in real time, according to the operational characteristics. Ingalls '869 teaches a method of varying compression, in real-time, to meet a pre-determined performance criteria. Ingalls '869 is concerned with the load of the system, in other words, the loudspeaker. Ingalls '869 does not teach a method for adjusting the amplifier of an audio system based off of the compression of the system. Furthermore, Ingalls '869 does not teach any method to have the user adjust the parameters of the audio system in order to meet the end-user's preferred settings.
U.S. Pat. No. 7,672,462, by named inventors Yamanashi, et. al. (“Yamanashi '462”), entitled, “Voice/musical sound encoding device and voice/musical sound encoding method,” teaches a system and method to protect against acoustic shock. Yamanashi '462 discloses a system comprising a method of receiving an input signal in the time domain and performing pattern analysis of the signal. The pattern analysis includes providing a filterbank with an oversampled signal representation, which a processor transfer. m.s. into a plurality of band signals in the frequency domain. Furthermore, the pattern analysis extracts characteristics, using both a fast average and slow average methodology, in order to arrive at parameters on which to form a decision. Yamanashi '462 does not disclose any methodology which measures compression, Crest Factor, Diminuendo Factor, or Dynamic Range. Additionally, Yamanashi '462 does not include any method or means for an end-user to adjust the audio output.
U.S. Pat. No. 7,583,137, by named inventors Pedersen, et. al. (“Pedersen '137”), entitled, “Power supply compensation,” teaches a method of compensating for power supply errors in switching amplifiers. In one embodiment, Pedersen '137 discloses a method of measuring power supply error, creating a compensation signal, and mixing the compensation signal with the input signal. Pedersen '137 does not address variable gain, compression, expansion, or dynamic range. Pedersen '137 does not mention user perception of compression, nor does it allow for user adjustment. Pedersen '137 does not disclose any methodology which measures compression, Crest Factor, Diminuendo Factor, or Dynamic Range. Lastly, Pedersen '137 does not include any method or means for an end-user to adjust the audio output.
U.S. Pat. No. 6,621,338, by named inventor Van Schyndel (“Van Schyndel '338”), entitled, “Gain determination for correlation processes,” teaches a method of adjusting the maximum level of voltage given to an electronic device (Load), by adjusting the output level, so that the supplied output voltage exceeds the maximum level of the Load for an amount of time greater than zero. Van Schydel '338 further discloses that the Load can be an analog-to-digital converter. Van Schydel '338 does not disclose any methodology which measures compression, Crest Factor, Diminuendo Factor, Dynamic Range, or user perception. Additionally, Van Schydel '338 does not include any method or means for an end-user to adjust the audio output.
U.S. Pat. No. 4,035,739, by named inventors Dickopp, et. al (“Dickopp '739”), entitled, “Amplifier with variable gain,” teaches a method of variable gain control that is frequency dependent, to overcome problems common with compander circuits. Dickopp '739 discloses a circuit for variable gain control in which the lower frequency cut-off is voltage-dependent, so that apparent noise will not be amplitude-modulated by the low-frequency signal energy density. Dickopp '739 does not disclose any methodology which measures compression, Crest Factor, Diminuendo Factor, or Dynamic Range. Additionally, Dickopp '739 does not include any method or means for an end-user to adjust the audio output.
U.S. Pat. No. 8,229,125, by named inventor Short (“Short '125”), entitled, “Adjusting dynamic range of an audio system,” teaches an automatic gain control method that has three inputs: output signal dynamic range, maximum output signal level, and minimum output signal level. The user must specify one of the three quantities. The second parameter is determined based off of the first, user-defined, parameter. The input is segmented, in the frequency domain, into frequency bands. The gain is adjusted in each band based off of the first and second parameters. Short '125 does not disclose any method or apparatus which accounts for the users perceptual preference. Furthermore, Short '125 does not disclose any relationship between the compression, Dynamic Range, the Crest Factor, and the Diminuendo Factor, which allows the end user to select the user's preferred point for the values. Lastly, Short '125 does not teach any user viewable measurement or analysis that compares compression, Dynamic Range, the Crest Factor, and the Diminuendo Factor.
U.S. Pat. No. 8,326,444, by named inventors Classen, et. al. (“Classen '444”), entitled, “Method and apparatus for performing audio ducking,” teaches a system and method for performing audio ducking between two or more signal. The first signal is analyzed, and its characteristic data, defined as its average level, is maintained for further analysis. A second signal is ducked with the first signal, by adjusting the second signal based on the characteristic data of the first signal. Classen '444 does not disclose any methodology which measures compression, Crest Factor, Diminuendo Factor, or Dynamic Range. Additionally, Classen '444 does not include any method or means for an end-user to adjust the audio output. Classen '444 is concerned solely with ducking two or more signals together based on relative levels.
U.S. Pat. No. 8,300,849, by named inventors Smirnov et. al. (“Smirnov '849”), entitled, “Perceptually weighted digital audio level compression,” teaches a digital audio method by taking an input signal; dividing it into frequency blocks; measuring its loudness using a perceptual filter within each block; determining its gain based on target loudness level and measure of loudness within each block; and determining a frequency-dependent gain amount using piecewise linear attack/release logic. Smirnov '849 does not teach a method for user adjustment of compression levels, nor does Smirnov '849 teach a method for determining Crest Factor, Lower Limit Tolerance, Clip Level, and allowing the user to adjust the same.
U.S. Pat. No. 7,848,531, by named inventors Vickers et. al. (“Vickers '531”), entitled, “Method and apparatus for audio loudness and dynamics matching,” teaches a method of defining and adjusting apparent loudness. An audio processor, used in conjunction with a compressor, divides the signal into time frames; determines apparent loudness within each time frame; weights the frames to emphasize louder frames, while including contribution of less loud frame; and adjusts the loudness of track based on calculation via nonlinear compression transfer function. Vickers '531 does not teach a user-defined adjustment of compression parameters, such as Crest Factor, Diminuendo Factor, and Clip Tolerance. Neither does Vickers '531 teach any method of comparing a pre- and post-processed dynamics signal.
The current prior art fails to provide a user-adjustable method of setting the level of audio dynamics, such as Effective Dynamic Range, Crest Factor, Diminuendo Factor, and Clip Level. Furthermore, the current prior art fails to provide adequate tools to measure and compare such factors, including a comparison of the input and output of a dynamics modifying device.